Such a slack adjuster, known in the art as a two-nut adjuster, may be found in U.S. Pat. No. 3,043,406. This slack adjuster may be defined as being of the single-acting, stroke-sensing type sensing the possible excessive slack due to wear on the application stroke (by comparing the real movement of for example a spindle with a control distance in the adjuster) and reducing the slack to the desired value on the return stroke.
In many instances, however, it is preferred to have a clearance-sensing, two-nut slack adjuster in which the effect of the elasticity part of the brake application stroke is removed, retaining the important advantage with a two-nut adjuster (as compared to the one-nut adjuster) being the very short dead stroke (for example less than 1 mm) due to the clutches, which may be compared to a dead stroke of 3 or 4 mm in a one-nut adjuster. This is of special importance for the outer dimensions of a brake unit, in which the slack adjuster is mounted, especially if there is a great leverage within the unit.